The days of America's Protestant "moral majority" could be drawing to a close, according to a new survey into the religious beliefs of the US public.

More than a quarter of US adults have left the faith in which they were brought up, with some choosing another religion but many embracing secularism, the survey found. Barely half of all Americans, 51 per cent, describe themselves as members of Protestant denominations while more than 16 per cent say they are atheist, agnostic or "nothing in particular."

Significantly for those concerned to understand the future of religious belief in the US, the biggest growth in secularism is among the young. One quarter of those aged 18 to 29 say they are not affiliated with any religion.

The Pew Forum on Religion and Public Life, a research organisation based in Washington, interviewed 35,000 adults aged 18 and over for the US Religious Landscape Survey. They found that the US remained strongly religious, but that the landscape is "diverse" and "fluid" with the US on the verge of becoming a minority Protestant country.

Researchers found that, if change from one Protestant group to another is included, 44 per cent of adults have switched religious affiliation.

The trends have surprised commentators in the US, which has traditionally been regarded as a God-fearing country, one of the most devout in the world since before the days of the 18th century Founding Fathers. Of the 204 who signed the Declaration of Independence and other key documents of that time, just three were Roman Catholic. Most were Episcopalian, with the next highest number being Presbyterian.

The survey found that the biggest losses due to fall-out were in the Catholic church, but these were largely offset by immigration from Latin America. One in ten Americans now describes themself as a former Catholic. The biggest families were those of Mormons and Muslims, respectively making up 1.7 per cent and 0.6 per cent of the adult population.

The report makes it clear that the US is not yet close to matching Europe's embrace of secularism. It concludes that the US "remains highly religious in its beliefs and practices."

But those who are losing their religion outnumber those finding a new faith by three-to-one.

The survey, carried out last year, found that 78.4 percent of the population identify themselves as Christian, including 51.3 per cent Protestant, 23.9 per cent Catholic, 1.7 per cent Mormon, 0.7 per cent Jehovah's Witness and less than 0.3 per cent Greek or Russian Orthodox. This compares with seven out of ten who described themselves as Christian in the 2001 census in the UK.

"The biggest gains due to changes in religious affiliation have been among those who say they are not affiliated with any particular religious group or tradition," the survey found.

Overall 7.3 per cent of the adult population say they were unaffiliated with any particular religion as a child.

Today, 16.1 per cent of adults say they are unaffiliated. "Sizeable numbers of those raised in all religions -- from Catholicism to Protestantism to Judaism -- are currently unaffiliated with any particular religion," the survey says.

Read the full report by clicking here